Margarine and spreads in the form of stick products are popular with many consumers who enjoy the serving size and shape of such products. To form a stick product, the plastic dispersion must contain from about 30 to 80% fat, stand up under its own weight at room temperature and be processible to be packed in a wrapper package. Additionally, consumer trends have been toward such stick products based on vegetable fats which spread easily, have a good melting behavior in both the mouth and on heated food items, contain a relatively high proportion of unsaturated fatty acids and also have a relatively low trans fatty acid level, preferably a level lower than 10%.
Conventional stick products containing much higher levels of trans fatty acids (i.e. greater than 10%) are cooled in scrapped surface heat exchanger units (A-units) before passing into a resting tube (B-unit). The conventional process thus provides a residence time in the resting tube so that the cooled oil or fat phase is substantially crystallized during the process rather than during storage.
With emulsions prepared from oil phases containing low levels of trans fatty acids, it was observed that conventional processing produced post-crystallization during storage and the packed product was brittle. Additional residence time is provided by the crystallizing units (C-unit) and the resting tube (B-unit). Therefore, the rotors within the crystallizing units (C-units) are conventionally run at relatively low shear speeds (e.g. less than 250 rpm) to add additional residence time to the processing of the stick products and avoid post-crystallization during storage. Even after providing the additional residence time it is difficult to obtain a uniformly crystallized stick product which has ideal packing hardness and is not brittle.
Traditionally, the residence time provided by passing through the C-units is only done after cooling the emulsion to a temperature where some crystals are formed and is not subjected to high shear. There therefore exists a need for a process to prepare a plastic dispersion having less than 10% trans fatty acid levels in the form of a stick which has a desirable hardness without brittleness and which exhibits good organoleptic properties.
Another object of the invention is to provide a commercially economical process which provides faster product packing and yet is flexible enough to be modified as required.